1. Field of the Invention
This invention relates to a process for depositing gallium oxide coatings on a flat glass substrate. More particularly, this invention relates to an atmospheric chemical vapor deposition process for producing gallium oxide coatings at high growth rates on flat glass using a coating precursor gas mixture comprising a gallium halide and an organicester.
2. Summary of Related Art
Gallium oxide coatings have been used, primarily, in connection with the production of semiconductor materials, for example, as a passivation layer for GaAs semiconductor wafers. It has also been formed by various methods on glass for uses in luminescent phosphor, solar cell, and deep-ultraviolet tranparent conducting oxide applications.
An article entitled “Synthesis of Homoleptic Gallium Alkoxide Complexes and the Chemical Vapor Deposition of Gallium Oxide Films”, M. Valet and D.M. Hoffman, Chem Mater, 2001, 13, 2135-2143, describes the use of low pressure chemical vapor deposition using organo-gallium and O2 precursors to form Ga2O3 films at substrate temperatures of 300-700° C. Deposition rates were reported to be less than 50 Å/min, i.e., less than 0.83 Å/sec.
Other investigations utilizing low pressure chemical vapor deposition have reported forming gallium oxide films, but also at a quite low deposition rates. Examples include:                Battiston et al. Thin Solid Films, 1996, 279, 115 (Growth rates of 117 Å/min i.e., 1.95 Å/sec.)        Ballarin et al. Inorg. Chim. Acta, 1994, 217, 71 (Growth rates not reported)        Minea et al. J. Mater. Chem. 1999, 9, 929. (Growth rates less than 3800 Å/min i.e., less than 63.3 Å/sec.)        
Gallium oxide thin films have also been produced using methods other than chemical vapor deposition.
U.S. Pat. No. 5,451,548 utilizes electron beam evaporation of single crystal high purity Gd3Ga5O12 complex compounds to form a Ga2O3 thin film. U.S. Pat. No. 5,474,851 describes producing a gallium oxide film by reactive vapor deposition in a vacuum plus oxygen, followed by tempering. U.S. Pat. No. 5,897,812 describes producing oxide/phosphors based on doped gallium oxides using RF magnetron sputtering for electroluminescent display materials.
It would be desirable to form gallium oxide films at essentially atmospheric pressure and to produce them at deposition rates compatible with time-critical manufacturing processes, for example, production of flat glass by the well-known float method. Those skilled in the art have continued to search for a method of producing gallium oxide films meeting the above-noted criteria in order to have available, affordable films for optical thin film stack designs.